Question

我有一个名为Lecture的模型，该模型对我的Courses模型具有外键。当我尝试添加一个讲座时，一切正常，但是当我尝试删除一个讲座时，很有可能会出现50％的错误。我不知道为什么可以删除某些内容，但是对于某些内容，我会收到以下错误消息：

这也是我的演讲模型：

class Lecture(models.Model):
    LECTURE_CHOICES = (
        ('Courses', 'Courses'),
        ('Seminars', 'Seminars'),
    )
    course = models.ForeignKey('Course', on_delete=models.CASCADE, null=True, related_name='lectures', )
    lecture_category = models.CharField(max_length=10, choices=LECTURE_CHOICES, default='Courses', )
    lecture_title = models.CharField(max_length=100, blank=True)
    content = models.TextField(blank=True)

    def __str__(self):
        return str(self.lecture_title)

class Course(models.Model):
    study_programme = models.ForeignKey('StudyProgramme', on_delete=models.CASCADE, null=True, blank=True)
    name = models.CharField(max_length=50, unique=True)
    ects = models.PositiveSmallIntegerField(validators=[MaxValueValidator(99)])
    description = models.TextField()
    year = models.PositiveSmallIntegerField(validators=[MaxValueValidator(99)])
    semester = models.IntegerField(choices=((1, "1"),
                                            (2, "2"),
                                            ), default=1)
    teacher1 = models.ForeignKey('TeacherData', on_delete=models.CASCADE, null=True, blank=True,
                                 verbose_name="Course Teacher", related_name='%(class)s_course_teacher')
    teacher2 = models.ForeignKey('TeacherData', on_delete=models.CASCADE, null=True, blank=True,
                                 verbose_name="Seminar Teacher", related_name='%(class)s_seminar_teacher')
    student = models.ManyToManyField('StudentData')
    slug = models.SlugField(max_length=150, unique=True)
    allow_upload = models.BooleanField(default=False)

    def __str__(self):
        return self.name

尝试删除对象时弹出NoneType错误

0 个答案: